This invention relates to the casting of metal strip. It has particular application to the casting of metal strip by continuous casting in a twin roll caster.
In a twin roll caster molten metal is introduced between a pair of contract-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow.
The setting up and adjustment of the casting rolls and the metal delivery and pool confinement components in a twin roll caster is a significant problem. The rolls must be accurately set to properly define an appropriate width for the nip, generally the order of only a few millimeters, and there must also be some means for allowing at least one of the rolls to move outwardly against a biasing force to accommodate fluctuations in strip thickness particularly during start up. The rolls may need to be changed between casts so as to allow a different width of strip to be cast and the rolls must be replaced if the casting surfaces are in any way damaged or deteriorate during casting. If the rolls have to be changed in sit-up, a significant amount of potential casting time is lost waiting for the casting components and the area surrounding them to cool. The new set of rolls, once in place, have to be calibrated prior to casting so that the nip width can be pre-set. When casting ferrous metals, it is necessary to preheat the refractory components of the metal delivery and pool confinement means to very high temperatures before casting commences. For these reasons it has been proposed to build twin roll casters with demonstrable components so that the rolls and preheated refractory components can be rapidly brought together into an operative assembly and casting started before the preheated components cool significantly. One example of a caster with moveable rolls and refractory components is disclosed in our Australian Patents 631728 and 637548 and corresponding U.S. Pat. Nos. 5,184,668 and 5,277,243.
The invention described in our Australian Patent Application 84244/98 enables a twin roll strip caster to be built with a modular construction in which the casting rolls are installed in a moveable module readily moveable into and out of the machine and in which the rolls can be accurately set up in the module so that the nip is preset and will be located accurately in the machine when the module is installed. This enables roll sets to be set up in advance in replacement modules for rapid changing of rolls between casts. However, proper positioning of the pool confinement side dams and proper adjustment of the mechanisms to apply the side dams to the ends of the rolls remains a problem, particularly if the size of the rolls is changed to allow a different width of strip to be cast.
A change of strip width requires a similar change in the width of the metal delivery nozzle and there must be an appropriate repositioning of the supports for the nozzle. There will generally also be a need to reposition other components which are dependent on the width of the casting pool, for example, any sealing elements which seal the casting pool chamber and any pool level sensor or camera installed at an end of the pool to examine the pool conditions during casting.
By the present invention the side dams and side dam applicators are mounted on a pair of carriages which can be moved in and out and preset to positions appropriate to the width of the casting pool. The side dams can thus be rapidly repositioned when the rolls are changed for any reason, for example, for a change of width of the strip to be cast. Moreover, the carriages can also be used to support other components which need to be adjusted according to the width of the casting pool, for example, nozzle end supports, casting pool seals and camera mountings.